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一、namespace

配置文件中namespace中的名称为对应Mapper接口或者Dao接口的完整包名,必须一致！

二、select

需求：根据id查询用户

1. 在UserMapper中添加对应方法

public interface UserMapper {//查询全部用户List<User> getUserList();//根据id查询用户User getUserById(int id);
}

2. 在UserMapper.xml中添加Select语句

    <select id="getUserById" parameterType="int" resultType="com.pojo.User">select * from mybatis.user where id = #{id}</select>

3. 测试类中测试

 @Testpublic void getUserById(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);User user = mapper.getUserById(1);System.out.println(user);sqlSession.close();}

三、insert

需求：给数据库增加一个用户

1. 在UserMapper中添加对应方法

public interface UserMapper {//查询全部用户List<User> getUserList();//根据id查询用户User getUserById(int id);//insert 用户int addUser(User user);}

2. 在UserMapper.xml中添加insert语句

 <insert id="addUser" parameterType="com.pojo.User">insert  into mybatis.user (id,name,pwd) value (#{id},#{name},#{pwd})</insert>

3. 在测试类中测试

 //增删改需要提交事务@Testpublic void addUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);int res = mapper.addUser(new User(6, "小李", "1233"));if(res>0){System.out.println("插入成功");}//提交事务sqlSession.commit();//很重要sqlSession.close();}

注意：增改删都必须要提交事务，即必须有：

 sqlSession.commit();

四、update

需求：修改用户的信息

1. 在UserMapper中添加对应方法

public interface UserMapper {//查询全部用户List<User> getUserList();//根据id查询用户User getUserById(int id);//insert 用户int addUser(User user);//修改用户int updateUser(User user);//删除用户int deleteUser(int id);
}

2. 在UserMapper.xml中添加update语句

    <update id="updateUser" parameterType="com.pojo.User">update mybatis.user set name=#{name},pwd=#{pwd} where id =#{id}</update>

3. 在测试类中测试

 @Testpublic void updateUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);mapper.updateUser(new User(2,"小王","1115"));sqlSession.commit();sqlSession.close();}

五、提交事务

需求删除一个用户信息

1. 在UserMapper中添加对应方法

public interface UserMapper {//查询全部用户List<User> getUserList();//根据id查询用户User getUserById(int id);//insert 用户int addUser(User user);//修改用户int updateUser(User user);//删除用户int deleteUser(int id);
}

2. 在UserMapper.xml中添加delete语句

<delete id="deleteUser" parameterType="int">delete from mybatis.user where id=#{id}</delete>

3. 在测试类中测试

  @Testpublic void deleteUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);mapper.deleteUser(5);sqlSession.commit();sqlSession.close();}

六、Map的使用

假设，我们的实体类，或者数据库中的表，字段或者参数过多，我们应该考虑使用Map!

1. UserMapper接口

    User addUser2(Map<String,Object> map);

2. UserMapper.xml

 <insert id="addUser" parameterType="map">insert  into mybatis.user (id,name,pwd) value (#{userid},#{username},#{password})</insert>

3. 测试

@Testpublic void getUserById2(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);Map<String,Object> map = new HashMap<String,Object>();map.put("helloid",1);mapper.addUser2(map);sqlSession.close();}

七、如何实现模糊查询？

List<User> userList = mapper.getUserLike("%李%");

<!--模糊查询--><select id="getUserLike" resultType="com.pojo.User">select * from mybatis.user where name like #{value}</select>

@Testpublic void getUserLike(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> userList = mapper.getUserLike("%李%");for (User user : userList) {System.out.println(user);}sqlSession.close();}